Decelerating system for touring vehicles

ABSTRACT

This system is intended for touring vehicles driven at a high speed corresponding to an engine shaft speed above 3,000 r.p.m. and preferably above 5,000 r.p.m. The engine is cooled by forced water circulation in a circuit comprising in series a pump, the engine and a radiator having a high heat dissipation capacity. The system comprises a hydraulic decelerator whose rotor runs permanently at a speed of at least the same order as engine shaft speed and whose diameter is less than 20 centimeters. The decelerator is connected in parallel to a part of the engine cooling circuit by means of a three-way two-position valve which when in one position sends all the water it receives to said part of the circuit isolating the decelerator, while when in its other position the valve sends all the water it receives to the decelerator inlet, isolating said circuit part.

United States Patent [4 1 Mar. 21, 1972 Bessiere [54] DECELERATINGSYSTEM FOR TOURING VEHICLES [72] Inventor: Pierre Etienne Bessiere,Golf-De-Saint- Nom-La-Breteche, France [73] Assignee: Labavia-S.G.E.,Paris, France [22] Filed: Sept. 16, 1969 [21] Appl. No.: 858,321

[30] Foreign Application Priority Data Sept. 17, 1968 France.......166527 Mar. 13, 1969 France... ..6907189 May 20, 1969 France..6916401 52 us. Cl. ..188/296, 192 3 TR [51] Int. Cl ..Fl6d 57/02 [58]Field of Search ..188/90, 90 A, 296; 192/3, 3 TR; 138/45, 46

[56] References Cited UNITED STATES PATENTS 1,915,547 6/1933 North et al..188/90 A 2,044,999 6/1936 Smith et al. ..188/90 A 2,170,128 8/1939 DeLa Mater. ....188/90 A 2,287,130 6/1942 Ramey ..188/90 A This system isintended for touring vehicles driven at a high Schweizer 188/90 APrimary Examiner-Milton Buchler' Assistant Examiner-John J. McLaughlinAttorneyFleit, Gipple & Jacobson ABSTRACT speed corresponding to anengine shaft speed above 3,000 rpm. and preferably above 5,000 r.p.m.The engine is cooled by forced water circulation in a circuit comprisingin series a pump, the engine and a radiator having a high heatdissipation capacity. The'system comprises a hydraulic decelerator whoserotor runs permanently at a speed of at least the same order as engineshaft speed and whose diameter is less than 20 centimeters. Thedecelerator is connected in parallel to a part of the engine coolingcircuit by means of a three-way two-position valve which when in oneposition sends all the water it receives to said part of the circuitisolating the decelerator, while when in its other position the valvesends all the water it receives to the decelerator inlet, isolating saidcircuit part.

19 Claims, 9 Drawing Figures Patehted March 21, 1972 3,650,358

4 Sheets-Sheet 1 III &

INVENTOR PIERRE E. BESSIERE Patented March 21 1972 I 3,650,358

4 Sheets-Sheet 2 {gig INVENTOR PIERRE E. BESSIERE Patented Mar ch 21,1972 4 Sheets-Sheet 4 Hill! HIHI INVENTOR PIERRE E. BESSIERE aa w JATTORNEYS DECELERATING SYSTEM FOR TOURING VEHICLES The invention relatesto systems adapted to decelerate a moving vehicle by applying adecelerating torque to one of the rotating elements of the transmissionline connecting the vehicle engine to the vehicle wheels; amongst suchsystems, the invention relates more particularly to those which arefitted to touring vehicles adapted to travel at high speedscorresponding to engine shaft speeds above 3,000 r.p.m., preferablyabove 5,000 rpm, and where the engine of the vehicle to be deceleratedis normally cooled by forced circulation of water in a circuitcomprising in series a pump, the vehicle engine and a radiator having ahigh heat dissipation capacity.

The invention also relates to vehicles fitted with such deceleratingsystems.

It is a main object of this invention to enable such devices to provideimproved deceleration of high-speed touring vehicles.

According to a main feature of the invention, systems of the kindspecified comprise: a hydraulic decelerator whose rotor runs permanentlyat a speed at least of the same order as engine shaft speed and whosediameter is less than 20 cm., preferably approximately 15 cm.; and meansfor connecting the decelerator in parallel to a part of the enginecooling circuit, the means comprising a three-way two-position valvewhich when in one position sends all the water it receives to the saidpart of the circuit, isolating the decelerator, while when in its otherposition the valve sends all the water it receives to the deceleratorinlet, isolating the said circuit part.

Preferably, decelerating systems of the kind specified use at least oneof the following two features:

According to one feature, relating to decelerating systems of the kindspecified used for vehicles having an internal combustion engine, thepower for operating the three-way valve is produced by the negativepressure in the engine induction pipe downstream of the adjustablethrottle member therein when such member is at least partly closed; anddriver-controlled means are adapted to use such power to operate thevalve.

According to the other feature, it also comprises a constrictiondisposed in the cooling circuit of the decelerator in the part betweenthe decelerator outlet and its place of connection to the normal enginecooling circuit, the constriction being such that the flow cross sectionwhich it presents to the liquid varies automatically, eithercontinuously or intermittently, in the same sense as the pressure ofsuch liquid.

In addition to these main features, the invention comprises otherfeatures which will be described in greater detail hereinafter withreference to the drawings and which are of course given merely toexplain the invention without limiting the same.

In the drawingsi HO. 1 is a view in axial section ofa deceleratoraccording to the invention, suitable for fitting to one end of theengine shaft of a touring vehicle;

FIG. 2 is a schematic view of a control circuit according to theinvention for the decelerator shown in FIG. 1;

FIGS 3 and 4 are diagrammatic views to an enlarged scale of anembodiment of the three-way valve of the circuit and of thevalve-actuating members, the same being shown in their two positionscorresponding to the decelerator being cut out of and into operation;

FIGS. 5 and 6 are graphs which help to show the advantage of one of thefeatures of the invention;

FIG. 7 is a view in axial section of an embodiment according to theinvention of the constriction in a decelerator of the kind described;

FIG. 8 is a view in axial section of another embodiment according to theinvention of such a constriction which in this case is in dual form, and

HG. 9 is a very diagrammatic view of a control system of use for adecelerating system according to the invention fitted with a dualconstriction of the kind shown in FIG. 8.

The conventional brakes used for lightweight and touring vehicles mustdecelerate the same from any speed right down to a standstill, ifrequired, and they achieve this by solid friction whether they are ofthe drum or disc kind. Brakes of this kind are very efficient andvirtually essential, but at high speeds they heat up rapidly and becomeunsatisfactory, particularly when applied repeatedly for prolongedperiods of time. This disadvantage is becoming increasingly widespreadas motorways increase in number and the maximum speeds attainable bymodern touring vehicles increase.

[t is conventional for heavy vehicles (trucks and coaches) to be fittedwith decelerators which help to decelerate the vehicles without stoppingthem completely; devices of this kind are useful more particularly onlong downgrades where conventional brakes would be likely to overheat.The decelerators operate without solid friction, being either hydraulicor electric (eddy current brakes), and so wear is greatly reduced.Unfortunately, devices of this kind, which are usually interposedbetween theclutch and the rear axle, have been too bulky and costly foruse in touring vehicles, the main reason for the bulkiness being therelatively slow speeds of rotor rotation (below 2,600 rpm.) and the hightorques required to decelerate heavy vehicles.

It has also been suggested that a heavy-vehicle hydraulic decelerator ofthis kind be supplied by the vehicle engine cooling water. This stepsuffers from the two following disadvantages:

Since the decelerator capacity to be filled is a relatively largevolume, decelerator response time is fairly slow, and this feature,although not a great disadvantage in the normal uses of suchdecelerators at low speeds and for long durations, would be adisadvantage for the braking of a vehicle travelling at very high speed,for a vehicle travelling at km./h. travels more than 40 m./sec.

More particularly, the cooling water may boil, since the heat-removalcapacity of the radiators normally used for heavy vehicles has no widemargins available for uses other than merely cooling of the engine, moreparticularly for dissipating heat evolved for a prolonged period of timeby a heat source other than the engine.

The applicants have observed first that the very high speeds attainableby the engines of high-speed touring vehicles (engine speeds of morethan 3,000 rpm. and possibly reaching and frequently exceeding 6,000rpm.) are suitable for producing relatively high braking torques bymeans of even very small hydraulic decelerators provided that the highspeeds are applied directly to the decelerator rotors. For instance, ata speed of 6,000 rpm. a braking torque of 15 m.kg. can be produced by ahydraulic decelerator having a rotor diameter of as little as 15 cm.Since small decelerators of this kind take up little space-and aretherefore of reduced cost they can be fitted below the hoods of touringvehicles, inter alia at one end of the vehicle engine crankshaft.

The applicants have also found that a system of this kind can withadvantage be supplied by the cooling water of the en- V gine, for thetwo disadvantages mentioned in the foregoing are greatly reduced or evenobviated for the following reasons:

Since the internal volume of the decelerator is small, it can be filledrapidly, more particularly if, as will be assumed hereinafter, theentire water flow is forced through it to give a brief response time,and

more particularly, there is no risk of the cooling water boiling sincethe brake applications" are much shorter than periods of running withdeceleration, and more particularly because, for a given engine powerand given load, the cooling circuits of touring vehicles are devised toremove much more heat-in any case several times more heat-than thecooling circuits of heavy vehicles, for the reason that:

the installed engine capacity per load unit is approximately 5-10 timesgreater in touring vehicles than in heavy vehicles, and

the use of petrol engines instead of diesel engines and the fact thatengine shaft speeds are higher lead to greater heating in touringvehicles.

In short, using a hydraulic decelerator at the very high speedsmentioned provides a number of associated advantages (high torque, smallsize, low cost, short response time, possibility of using the enginecooling water to supply the decelerator without risk of the waterboiling) which make it very attractive to use a system of this kind tobrake a high-speed tour ing vehicle. The system can very readily reducethe high speeds of such vehicles by very effective progressivedecelerations down to a medium speed at which the conventional brakescan be used satisfactorily.

The safety provided by this form of deceleration at high speeds isoutstanding, particularly since, although it is so effective, there isno risk of skidding, for the decelerating torque provided by a hydraulicdecelerator is relatively low at low speeds of rotation and shouldtheoretically drop to zero when the wheels lock; the device thereforehas a self-regulating action, the decelerating torque automaticallydecreasing immediately the wheels lock due to excessive deceleration andvice versa.

FIG. 1 shows an embodiment of a hydraulic decelerator which is of useaccording to the invention but which does not limit the same. Thedecelerator comprises a rotor forming a centrifugal pump and comprisinga semitoroidal shell 1 whose base is open at a place 1 and which isbraced by blades 2 which are radial or inclined in the direction ofrotation to increase the braking effect. The decelerator also includes astator comprising: a semitoroidal socketedshell 3 disposed axiallyopposite the rotor; and a cover 4 around the rotor. The rotor is rigidlysecured to a shaft portion 5 disposed at the ends of the vehicle engineshaft, as a rule, the crankshaft; the shaft portion 5 is centeredrelatively to the engine frame 6 by a roller bearing 7 sealed by two cupseals 8, beyond which the shaft portion 5 overhangs. A rotating gasket 9sliding on a stationary ring 10 provides sealing-tightness between therotor and the engine frame 6.

The sockets of the stator shell 3 are designed to collect the liquidstreams emitted by the tips of the blades 2 and to re-inject suchstreams into the small-diameter zones of the blades 2 so as to producevortices tending to brake the rotor.

The cover 4 comprises: a liquid inlet 11 which is offset from the rotoraxis, so as to reduce the overall axial size of the decelerator; and anoutlet 12 for the liquid which escapes radially between the blades 2 andthe sockets 3 to an annular chamber 13 of the stator. The cover insidesurface extends very close to the external profile of the rotor so as toreduce leakages of liquid going directly from the inlet 11 to thechamber 13 without having passed through the toroidal enclosure (2, 3)where the decelerating torque is produced.

The connection between the inlet 11 and such enclosure is by way ofpassages 2 bounded by the upstream tips of the blades 2 and extendingthrough the open part 1,.

A decelerator of this kind does not require accurate machiningoperations and is rugged and cheap.

To operate the decelerator as and when required, the same is suppliedwith the entire water flow used to cool the vehicle, such water normallybeing circulated by a pump in a closed circuit through the engine and acooling radiator consecutively.

FIG. 2 shows the hydraulic decelerator 14, engine 15 of the vehicle anda radiator 16 cooled by a fan 17. As in conventional cooling circuitsthe water is moved by a pump 18 seriatim from the engine to theradiator, after heating, through a line 20, and from the radiator to theengine, after cooling, through a line 19. in the present case the line20 has a threeway two-position valve 21 which in one position completesthe line 20 and which in the other position diverts all the flow throughthe valve to supply a decelerator inlet line 22.

A decelerator outlet line 23 is connected to the line 20 at a place 24slightly downstream of valve 21. if that section of the line 20 whichseparates the valve 21 from the place 24 is given the reference 29, itcan be stated that the decelerator 14 and its inlet and outlet lines 22,23 are shunted across the section 29.

To prevent any flowback of water from the place 24 to the decelerator,the line 23 joins the interior of the line 20 in the direction of normalwater flow in the line 20. Of course, other means could be used toachieve the same result, such as a non return valve or a second valvecoupled with the first valve, but the suggestion made here is veryrugged and economical.

The circuit also comprises: a narrow line 25 connecting the deceleratorto the normal cooling circuit at a place 26 disposed upstream of thepump 18, the connection being such that the normal cooling water flowhas an aspirator effect on the contents of the line 25 and thus helps toempty the decelerator when the valve 21 is in its normal nonbrakingposition; and a narrow line 27 connecting the decelerator to the top ofan expansion tank 28-if the ordinary cooling circuit is a closed circuitand has an expansion tankto enable gas from the expansion tank to helpdrain the decelerator of water and to help fill the decelerator withwater by removal from the decelerator of the gas therein to theexpansion tank.

A circuit of this kind operates as follows: ,7

When the valve 21 is in the position in which it completes the line 20,the water normally in a closed circuit through the radiator and theengine. The aspirator effects set up at the places 24, 26 empty thedecelerator completely so that the same produces no disturbing residualtorque.

To decelerate the vehicle, the valve 21 is changed over to the positionwhich is shown in FIG. 2 and in which all the cooling water goes throughthe decelerator so that the same is connected in series in the normalcooling circuit.

Most of the water leaving the decelerator then passes through theradiator and is cooled therein, but the water flow ing through the line25 is not cooled in this way. This is not a disadvantage in practicesince the latter flow, although ensuring rapid decelerator emptying, isvery small in relation to the total flow.

A control circuit of this kind has many advantages for small high-speeddecelerators used in light vehicles. More particularly, the controlresponse time is very short, for when the valve 21 is placed in itsoperative position the delivery from the circulating pump is compelledto flow through the decelerator, in contrast to systems in which thedecelerator is just connected in parallel to the cooling circuit. Also,the cooling water delivery is maximum since it is driven not just by theordinary circulating pump but also by the decelerator which is devisedas a centrifugal pump. This maximum delivery (e.g., of theorder of fromto liters/min.) always achieves production of the maximum deceleratingtorque corresponding to engine speed at the particular time concerned,and maximum heat removal. in other words, when a brief application ismade at high speed, the resulting decelerating torque is not limited bywater temperature, because of the heat inertia of the total volume ofcirculating water, and in prolonged deceleration the decelerating torqueis limited only by the heat removal capacity of the radiator and, asalready stated, this capacity is very high in the case of touringvehicle radiators.

The valve 21 can be operated either by being directly coupled to aspecial control pedal or lever or to the conventional brake pedal oraccelerator pedal. Unfortunately, connections of this kind are difficultto embody and unreliable in operation; preferably, therefore, the powersource for this control, in the preferred case in which the vehicleengine is an internal combustion engine, is the negative pressure in theengine induction pipe downstream of the throttle member or butterfly insuch pipe, the bringing of this negative pressure into operation beingdependent on a driver-operated control. Consequently, the deceleratorcomes into operation only when permitted to do so deliberately by thedriver and when the negative pressure has a high enough absolute value,a factor presupposing a reduced fuel supply to the engine (butterflyvalve closed completely or almost completely) and a high enough vehiclespeed. Clearly, therefore, this particular form of control is verysuitable for the purposes of the invention, since the main requirementis that the control be satisfactory at very high speeds.

A control of this kind is shown in FIGS. 3 and 4, where valve 21 iscontrolled by a system 31 responding to the negative pressure in theengine induction pipe 51 at a place 53 downstream of throttle member 52,communication between system 31 and pipe 51 being by way of means 32under the driver's control. More particularly, the system 31 is such asto cut in the decelerator, under the control of the means 32, only whenthe absolute value of such negative pressure exceeds a predeterminedthreshold corresponding to closure of the butterfly 52 and to an enginespeed above a predetermined threshold.

In the embodiment shown in FIGS. 3 and 4, the three-way two-positionvalve 21 has a chamber 34 in permanent communication with the'watersupply line 20, the lines 29, 22 terminating in chamber 34 by way ofcoaxial seats 35, 36 respectively, the seats cooperating with respectivelids 37, 38 mounted on a single rod 39. I

The system 31 comprises a variable-volume chamber 40 bounded by adiaphragm 41 (or other movingor deformable member adapted to close thechamber 40 hermetically) connected to rod 39. A cover 42 crimped to the'casing of chamber 40 clamps the periphery of diaphragm 41 and is formedwith an aperture 43 via which atmospheric pressure is operative on thatside of diaphragm 41 which is remote from chamber 40. A spring 50 actingon rod 39 and/or diaphragm 41 opposes the action of the negativepressure in chamber 40. The means 32, which comprise a nonretum valve 44or some other moving closure member, are disposed in a line 45 adapted,when the valve 44 is open, to connect chamber 40 to place 53 (thedirection of flow in induction pipe 51 is diagrammatically representedby an arrow in each of FIGS. 3 and 4).

The driver-controlled means 32 can be either entirely independent of anyother vehicle control or can be subject to some other control such asthe accelerator pedal operating the butterfly 52, the conventional brakepedal or the clutch pedal. In the case of accelerator pedal control, themeans 32 can be such that the driver can operate the valve 44 directlyby hand (or foot), e.g., via a push button (not shown) placed directlyon the vehicle steering wheel- (in the commonest case of a roadvehicle), so that the driver does not have to release the wheel tooperate the valve 44.

Preferably, however, the means 32 are so devised in both the caseshereinbefore set forth as to be operable by a solenoid valve in the forminter alia of an electromagnet 46 which operates valve 44 against theforce of a return spring 47. Preferably, the circuit arrangement is suchthat the electromagnet 46, when energized by a power supply 48 via acontactor 49, opens the valve 44 and therefore connects chamber 40 tothe place 53 in the engine induction pipe 51, whereas the spring 47tends to isolate the chamber 40 when contactor 49 de-energiseselectromagnet 46.

In the case of independently operated control means 32, the contactor 49can be placed on the vehicle instrument panel so that the driver canpermit or override operation of the electromagnet 46 and therefore ofthe decelerator.

In the case of means 32 subject to some other control of the vehicle, afirst suggestion is to embody the contactor 49 by a microswitch disposednear the accelerator pedal and adapted to energize electromagnet 46 onlywhen the accelerator pedal is in a position corresponding to minimumopening of butterfly 52. Consequently, when the vehicle is running onlevel ground or down a slight downgrade, the driver retains thepossibility of lifting his foot operating the accelerator pedal almostcompletely without cutting in the decelerator, for the contactor 49 isnot then operated by the pedal, and so valve 44 stays closed andprevents the negative pressure from reaching the diaphragm 41. However,if the driver releases the accelerator pedal completely the deceleratorcuts in, so that the line 45 is made continuous provided that enginespeed is high enough for the negative pressure reaching the diaphragm 41to be sufficient to overcome the force of the spring 50.

A second suggestion is to embody the contactor 49 by a microswitchplaced near the ordinary brake pedal so that the contactor allowselectromagnet 46 to be energized only when 6 the'driver operates thebrake pedal, preferably duringthe dead part of the brake pedal travelprior to application of the ordinary brake. This is advantageous in thecase of a vehicle in which the decelerator is required to operate onlywhen the driver operates the brake pedal, inter alia for town driving sothat gear-changing operations are not disturbed.

A third suggestion is to embody the contactor 49 as a microswitchcontrolled by the clutch pedal and adapted to deenergize theelectromagnet 46 and therefore prevent the decelerator from operating,when the driver operates the clutch pedal.

At least two of the controls just outlined for energin'ng theelectromagnet can be combined to form the means 49. Ad-

vantageously, one such mixed control 49 comprises a first single controlin the form first contactor connected to the a ccelerator pedal. Thesecond single control can comprise a second contactor in series with thefirst contactor and mountedon the instrument panel for direct driveroperation; consequently, when driving in town'the driver can ensure thatthe decelerator does not operate whenever he raises his foot off theaccelerator pedal. The second single control can also comprise a secondcontactor in series with the first contactor and controlled, aspreviously mentioned, by the clutch pedal; 7

this ensures that when the driver lifts his foot off the accelerator forgear changing, the decelerator does not operateand gear changing is notimpaired by the normal deceleration,

more particularly in the case of changing up, although due to the slightdelay of the accelerator in responding this deceleration is barelyperceptible.

- Other improvements in or relating to the decelerating facilities'hereinbefore described will now be described, since it may 7 be useful:

to, further shorten response timei.e., the time between operation of thethree-way valve and production of an appreciable decelerating effect(this time is normally about 1 sec. in systems of the kind of interesthere); i

to arrange for the decelerators to be considerably effective even at lowspeeds, since in the absence of any special action the braking torqueoutput by a hydraulic decelerator decreases considerably when the speedof rotation of its rotor and its internal pressure decrease.

In the present case in which the decelerator rotor and the circulatingpump are engine-driven, the pressure in the hydraulic cooling circuit(19, 22, 23, 20) decreases with'engine speed, and so the deceleratorbraking torque decreases very considerably when engine speed decreases.One way of increasing the torque at low speeds would be to increase thepressure in the hydraulic circuit by the provision of a constriction atthe decelerator outlet. Unfortunately, thisstep would systematicallyincrease pressure even at high speeds, with the risk of producingdecelerating torques in excess of the limits of adhesion of the brakedwheels or the limits of clutch slip at high speeds.

Consequently, a constriction 54 is provided at the output of thedecelerator 14 and is so devised that the opening cross section which itpresents to the flow of liquid varies automati cally, continuously orintermittently, in the same sense as the pressure of the liquid orwhichcomes to the same thingas the rate of flow of such liquid once theoperating condition has been established. Consequently, when there is noliquid in the decelerator the constriction has a minimum opening crosssection, possibly zero opening cross section, and it fills very rapidlyimmediately after the corresponding actuation via the three-way valve;it is found that the presence of this downstream constriction canreadily double the speed of decelerator filling. 1

Also, the presence of the constriction increases the pressure of thevolume of liquid disposed immediately upstream of the constrictioni.e.,in the decelerator-in proportion as the opening cross section of theconstriction is smaller; consequently, at high speeds, corresponding toa large opening cross section of the constriction, there is no risk ofan excessive decelerating torque which might lock the vehicle wheels;

also, the decelerating torque produced at relatively low speeds,corresponding to a relatively small flow cross section through theconstriction, is increased appreciably to an extent such that it becomesperceptible and effective, so that the facility works over a wide rangeof speeds and not just at very high speeds.

To show the usefulness of automatic variation of the constriction crosssection, it can be stated that, with a constriction whose cross sectionremains at 65 mm. the decelerating torque drops from 15 to 0.8 m.kg.when the speed of decelerator rotor rotation drops from 5,000 to 2,500r.p.m., ceteris paribis, whereas if the constriction cross sectiondecreases from 65 to 20 mm. approximately during the same time that thespeed drops from 5,000 to 2,500 r.p.m. the braking torque decreases onlyfrom l5 to 9.1 m.kg. in the same conditions.

These results can be gathered from the graph which is shown in FIG. 5and in which the braking torque C expressed in m.kg. is plotted alongthe ordinates and the speed V in r.p.m. is plotted along the abscissae.Curve 55 of the graph shows variations of the torque C in dependenceupon speed V for a fixed constriction cross section of 65 mm. (circularorifice of approximately 9 mm. diameter) at the decelerator outlet; itcan be seen in this case that the torque drops from about m.kg. (pointA) to less than I m.kg. (point B) for a speed reduction from 5,000 to2,500 r.p.m. Curve 56 corresponds to a fixed constriction crosssectionof 7 mm. (circular orifice of 3 mm. diameter); in this case, the torqueclearly becomes excessive at speeds above 3,500 r.p.m. Curve 57corresponds to a variable constriction according to the invention whosecross section decreases from 65 mm. to about mm. (circular orifice 5 mm.in diameter) simultaneously as thespeed drops from 5 ,000 to 2,500r.p.m.; this curve shows clearly that the torque is still appreciable at2,500 r.p.m., since it is still above 9 m.kg. (point C).

In more general terms, the system fitted with the variable constrictionoperates as follows:

At low engine speeds the delivery of water from the circulating pump issmall and the opening of the constriction is at a minimum. As enginespeed increases, the water delivery increases too and so, unless theopening of the constriction increased simultaneously so as to keep thepressure substantially constant, the pressure would tend to increase. Anautomatic regulation which largely compensates for speed-dependenttorque variations is therefore provided.

Another considerable advantage of having a variable constriction at thedecelerator outlet is that it reduces the decelerator response time;when the decelerator is out of operation the water pressure therein iszero and the cross section of the constriction at the decelerator outletis minimum, and so when the three-way valve is changed over to energizethe decelerator, the same fills very rapidly and the discharge orificeopens gradually as filling proceeds.

This result can be seen in the graph which is shown in FIG. 6 and inwhich the decelerating torque C expressed in percentages of its maximumoperating value is plotted along the ordinates and the response time Iin seconds calculated from the time at which the three-way valve isoperated is plotted along the abscissae. The two curves 58, 59 bothcorrespond to the setting up of a rated or operating torquecorresponding to 4,000 r.p.m., curve 58 being for a constant crosssection decelerator outlet while curve 59 is for a downstreamconstriction having an automatically varying cross section. Clearly,after 0.4 sec. the decelerating torque has risen to 16 percent of itsrated value in the first case (point D) and to 40 percent of its ratedvalue in the second case (point E)-a considerable advantage in cases inwhich the facility is required to decelerate a vehicle travelling atvery high speed, since a fastmoving vehicle travels a considerabledistance in half a second.

Another advantage is that increasing the constriction cross sectionhelps to increase the water delivery and simultaneously to increase therated torque and therefore the'braking power, so that water delivery isadapted to required power at all engine speeds. This feature cuts outtemperature variations due to operation of the decelerator, an advantagefor the engme.

The constrictions having an automatically variable cross section ashereinbefore described can be embodied in any appropriate fashion, forinstance, as a calibrated-spring nonreturn valve or as a pivoted flapbiased resiliently towards its closed position and so devised that theliquid pressure on the upstream side tends to open it. Another possibleform for such a constriction is a sliding lid whose position can vary independence upon the upstream pressure, the same acting on the lidthrough an appropriate sampling line; alternatively, the open- 7 ing ofthe constriction could be controlled directly not by the liquid pressurebut by some other parameter, such as engine speed, varying in the samesense as the liquid pressure.

Very advantageously, however, the constriction is embodied by means of aresilient diaphragm 60 (FIG. 7) made of rubber or some other elastomericsubstance and pierced with a calibrated orifice 61. Preferably, tofacilitate the deformation of such a diaphragm, the edge of thecalibrated orifice has the general shape of a nozzle converging towardsits downstream end. The elastomeric substance must be able to undergoconsiderable stretch so that the orifice diameter can vary in operationfrom its ordinary size to three times its ordinary size or even more.The material must be temperature-resistant (often, the temperature isnear the temperature of boiling water) and must be able to withstandchemical attack by the cooling liquid and must be non-tearing.

Conveniently, the decelerating systems hereinbefore described can beadjustable instead of being just two-step action devices, for even ifthe vehicle is travelling very fast the driver may require only arelatively small decelerating torque, for instance, sufficient to keepvehicle speed constant on a downgrade or to brake the vehicle verygently and gradually.

Accordingly, the variable constriction comprises a number-preferablytwo-of constrictions respectively associated with lines connected inparallel to the decelerator outlet, all the lines except one beingadapted to be made inoperative by appropriate valves.

The advantage of such a feature will be readily apparent; the pressurein the decelerator is smaller in proportion as the total cross-section,and therefore the number, of the constrictions offering a passage to theliquid leaving the decelerator is larger.

Consequently, such pressure--and the corresponding deceleratingtorque-can be controlled as required by varying the numberofconstrictions in operation; more particularly, if there are twoconstrictions, the driver can choose between a first relatively gentledeceleration, similar to the deceleration provided by engine braking,when the two constrictions in parallel are used, and a second strongerdeceleration, for which only one of the two constrictions is used, theother being rendered inoperative by closure of a valve.

The constrictions can have opening cross sections which are either fixedor automatically variable in the manner hereinbefore described; in thecase of fixed cross sections, the same regulating effect as previouslyprovided continuously by a single variable constriction is obtained butintermittently, the bringing into operation of an increasing number offixed-section constrictions having the same result as the progressiveopening of a single constrictioni.e., increased water circulation.

The various constrictions can be cut into and out of operation by anyappropriate mechanical, electrical, pneumatic or hydraulic means.

The embodiment shown in FIGS. 8 and 9 comprises two constrictions 54,,54 connected in parallel to two lines 62, 63 respectively, the line 62forming a part of the line 23 and the line 63 being closable by a valve64. It is assumed in this embodiment that the engine is an internalcombustion engine and the power source for operating the valve 64 is thenegative pressure in the engine induction pipe 51 at the place 53downstream of the throttle valve 52; this negative pressure can closevalve 64 by attracting a diaphragm 65 connected to valve 64 against theforce of a return spring 66.

As previously, such negative pressure is also used to operate the valve21 and is in fact used to operate the desired member (valve 21 or valve64) only when the driver expresses the deliberate intention for thisoperation, inter alia by electrically energizing a solenoid valve (32,67) disposed in a line (45, 68) for connecting the place 53 to therequired member.

Energization can be achieved very simply by placing the handle 69 (FIG.9) of a switch to the appropriate position; the three positionsdiagrammatically shown as a, b and c in FIG. 9 for the handle 69correspond to zero decelerating torque, to a reduced decelerating torque(energization only of solenoid valve 32, corresponding to operation ofthe decelerator and two constrictions 54,, 54 and maximum decelerationtorque (energization of the two solenoid valves 32, 67, corresponding tooperation of the decelerator with closure of valve 64i.e., use solely ofconstriction 54,), respectively.

In a variant the two solenoid valves can be controlled by differentmembers, the first being, with advantage, energized just by release ofthe accelerator pedal and the second being energized by initiation ofoperation of the brake pedal.

Clearly, and as the foregoing shows, the invention is not limited tothose of its embodiments and uses which have been more particularlydescribed, but covers all variants.

I claim:

1. A system for decelerating a touring vehicle driven at a high speedcorresponding to an engine shaft speed above 3,000 r.p.m., the vehicleengine normally being cooled by forced liquid circulation in a circuitcomprising in series a pump, the vehicle engine and a radiator having ahigh heat dissipation capacity, wherein the system comprises: ahydraulic decelerator having a rotor which is adapted to be connected tothe engine shaft so as to run permanently at a speed at least of thesame order as engine shaft speed, the diameter of said rotor being lessthan cm., inlet and outlet means connecting the decelerator in parallelto a part of the engine cooling circuit, said means comprising upstreamof said part of said engine cooling circuit a three-way two-positionvalve arranged when in one position to send all the liquid it receivesto said part of the circuit, isolating the decelerator, and when in itsother position to send all the liquid it receives to the inlet means,isolating said circuit part, and a constriction means in the outletmeans for automatically varying the flow cross section which it presentsto the liquid in the same sense as the pressure ofthe liquid.

2. A system according to claim 1, including control means for thethree-way valve arranged to be automatically operated by the beginningof the instinctive movement of the right foot ofthe driver at the momentwhen he wishes to decelerate.

3. A system according to claim 2, wherein the control means are operatedby the end of the release of the accelerator pedal.

4. A system according to claim 2, wherein the control means are operatedby the beginning of the depression of the brake pedal.

5. A system according to claim 1, wherein said engine shaft speed isabove 5,000 r.p.m.

6. A system according to claim 1, wherein said rotor-diameter isapproximately 15 cm.

7. A system according to claim 1, the vehicle engine being an internalcombustion engine including an induction pipe with an adjustablethrottle member therein, said system further comprising power means forderiving power from the negative pressure in the engine induction pipedownstream of the adjustable throttle member therein when said throttlemember is at least partly closed, and for using this derived power tooperate the three-way valve.

8. A touring vehicle comprising a decelerating system according to claim1.

9. A system as set forth in claim 1, the vehicle engine being aninternal combustion engine'including an induction pipe with anadjustable throttle member therein, said system further comprising powermeans for deriving power from the negative pressure in the engineinduction pipe downstream of the adjustable throttle member therein whensaid throttle member is at-least partly closed, and for using thisderived power to operate the threeway valve; and driver-controlled meansfor connecting and disconnecting said power means to the induction pipedownstream of the adjustable throttle member therein when said throttlemember is at least partly closed in order to bring said power means intoand out of service respectively.

10. A system as set forth in claim 9, wherein said power means comprisea chamber connected via 'a line to a place in the engine induction pipedownstream of the throttle member, and a movable member mounted in saidchamber to be moved by the pressure in said chamber, said movable memberbeing operatively connected to said three-way valve; and saiddrivercontrolled means comprise a driver-controlled solenoid valvedisposed in said line.

11. A system as set forth in claim 10, wherein the drivercontrolledmeans comprise a switch which is accessible to the driver and connectedin the energizing circuit for the solenoid valve.

12. A system as set forth in claim 11, wherein the drivercontrolledmeans comprise an electric switch which is connected in the energizingcircuit for the solenoid valve and whose operation is controlled by adriver control different from said previously mentioned switch which isaccessible to the driver.

13. A system as set forth in claim 12, wherein the drivercontrolledmeans comprise at least two switches connected to two different controlactions and connected in series in the energizing circuit for thesolenoid valve.

14. A system as set forth in claim 1, wherein at least some of thelast-mentioned part of the decelerator cooling circuit comprises anumber of parallel-connected sections each having a constriction meansand, means being provided for selectively closing and opening all thevarious sections except one.

15. A system as set forth in claim 14, wherein the number ofparallel-connected sections is two.

16. A system as set forth in claim 15, the vehicle engine being aninternal combustion engine having an induction pipe containing anadjustable throttle member wherein one of the two parallel-connectedsections has a nonretur'n valve adapted to be operated, under drivercontrol, by the negative pressure which exists in the engine inductionpipe downstream of the adjustable throttle member therein.

17. A system as set forth in claim 14, wherein the constriction means isembodied by a diaphragm in the form of an orifice in a membrane made ofelastomer.

18. A system as set forth in claim 17, wherein the edge of the orificehas the shape of a nozzle converging in the downstream direction.

19. A system as set forth in claim 1, wherein control of the automaticvariations of the passage cross section of the constriction is provideddirectly by the liquid pressure.

1. A system for decelerating a touring vehicle driven at a high speedcorresponding to an engine shaft speed above 3,000 r.p.m., the vehicleengine normally being cooled by forced liquid circulation in a circuitcomprising in series a pump, the vehicle engine and a radiator having ahigh heat dissipation capacity, wherein the system comprises: ahydraulic decelerator having a rotor which is adapted to be connected tothe engine shaft so as to run permanently at a speed at least of thesame order as engine shaft speed, the diameter of said rotor being lessthan 20 cm., inlet and outlet means connecting the decelerator inparallel to a part of the engine cooling circuit, said means comprisingupstream of said part of said engine cooling circuit a three-waytwo-position valve arranged when in one position to send all the liquidit receives to said part of the circuit, isolating the decelerator, andwhen in its other position to send all the liquid it receives to theinlet means, isolating said circuit part, and a constriction means inthe outlet means for automatically varying the flow cross section whichit presents to the liquid in the same sense as the pressure of theliquid.
 2. A system according to claim 1, including control means forthe three-way valve arranged to be automatically operated by thebeginning of the instinctive movement of the right foot of the driver atthe moment when he wishes to decelerate.
 3. A system according to claim2, wherein the control means are operated by the end of the release ofthe accelerator pedal.
 4. A system according to claim 2, wherein thecontrol means are operated by the beginning of the depression of thebrake pedal.
 5. A system according to claim 1, wherein said engine shaftspeed is above 5,000 r.p.m.
 6. A system according to claim 1, whereinsaid rotor-diameter is approximately 15 cm.
 7. A system according toclaim 1, the vehicle engine being an internal combustion engineincluding an induction pipe with an adjustable throttle member therein,said system further comprising power means for deriving power from thenegative pressure in the engine induction pipe downstream of theadjustable throttle member therein when said throttle member is at leastpartly closed, and for using this derived power to operate the three-wayvalve.
 8. A touring vehicle comprising a decelerating system accordingto claim
 1. 9. A system as set forth in claim 1, the vehicle enginebeing an internal combustion engine including an induction pipe with anadjustable throttle member therein, said system further comprising powermeans for deriving power from the negative pressure in the engineinduction pipe downstream of the adjustable throttle member therein whensaid throttle member is at least partly clOsed, and for using thisderived power to operate the three-way valve; and driver-controlledmeans for connecting and disconnecting said power means to the inductionpipe downstream of the adjustable throttle member therein when saidthrottle member is at least partly closed in order to bring said powermeans into and out of service respectively.
 10. A system as set forth inclaim 9, wherein said power means comprise a chamber connected via aline to a place in the engine induction pipe downstream of the throttlemember, and a movable member mounted in said chamber to be moved by thepressure in said chamber, said movable member being operativelyconnected to said three-way valve; and said driver-controlled meanscomprise a driver-controlled solenoid valve disposed in said line.
 11. Asystem as set forth in claim 10, wherein the driver-controlled meanscomprise a switch which is accessible to the driver and connected in theenergizing circuit for the solenoid valve.
 12. A system as set forth inclaim 11, wherein the driver-controlled means comprise an electricswitch which is connected in the energizing circuit for the solenoidvalve and whose operation is controlled by a driver control differentfrom said previously mentioned switch which is accessible to the driver.13. A system as set forth in claim 12, wherein the driver-controlledmeans comprise at least two switches connected to two different controlactions and connected in series in the energizing circuit for thesolenoid valve.
 14. A system as set forth in claim 1, wherein at leastsome of the last-mentioned part of the decelerator cooling circuitcomprises a number of parallel-connected sections each having aconstriction means and, means being provided for selectively closing andopening all the various sections except one.
 15. A system as set forthin claim 14, wherein the number of parallel-connected sections is two.16. A system as set forth in claim 15, the vehicle engine being aninternal combustion engine having an induction pipe containing anadjustable throttle member wherein one of the two parallel-connectedsections has a nonreturn valve adapted to be operated, under drivercontrol, by the negative pressure which exists in the engine inductionpipe downstream of the adjustable throttle member therein.
 17. A systemas set forth in claim 14, wherein the constriction means is embodied bya diaphragm in the form of an orifice in a membrane made of elastomer.18. A system as set forth in claim 17, wherein the edge of the orificehas the shape of a nozzle converging in the downstream direction.
 19. Asystem as set forth in claim 1, wherein control of the automaticvariations of the passage cross section of the constriction is provideddirectly by the liquid pressure.